1. Field of the Invention
This invention relates to an ink jet black ink, an ink set, an ink jet recording method, an ink cartridge, a recoding unit, and an ink jet recording apparatus.
2. Related Background Art
The ink jet recording method is a recording method of applying a small ink droplet by a working principle of various types to any one of recording medium such as paper to record images, letters or characters and so forth. Also, the ink jet recording method has characteristic features that high-speed, low-noise and multi-color printing is performable with ease, recorded patterns can enjoy a great versatility, and also development and fixing are unnecessary. Accordingly, in recent years, as a recording apparatus which forms a variety of images, such a method has rapidly come into wide use in various uses including information equipment. Moreover, images formed by a multi-color ink jet recording method can also provide record which bears comparison with multi-color print formed by a graphic method and prints formed by a color photographic method. When printed on a small number of sheets, such images are more inexpensive than usual multi-color print or photographic prints. For these reasons, the ink jet recording method is being widely applied up to a field of full-color image recording.
In recent years, as recording mediums for ink jet recording, recording mediums are also used in which a porous material such as alumina or silica is used as an ink receiving material in order to achieve image quality comparable to, or higher than, that of silver halide photographs. In particular, a recording medium making use of an alumina hydrate can promise good fixing of coloring materials having negative electric charges in ink, because the alumina hydrate has positive electric charges, and can provide well color developed images. Thus, such a recording medium has an advantage such that it is more preferable than conventional recording mediums in terms of image quality and glossiness especially in full-color images.
Inks used in the ink jet recording method are required to have reliability such as ink jet suitability, and besides, to provide recorded images with a sufficient optical density, to have good drying characteristics, to cause no blur in recorded images, to cause no flow-out of recorded images even when come into contact water, alcohol or the like, to make recorded images have a good weatherability, and so forth. In particular, it is very strongly required that recorded images have a good weatherability. The weatherability is, that is to say, the image fastness that recorded images undergo no color change or discoloration due to sunlight or illumination of various types (i.e., light fastness), or that recorded images undergo no color change or discoloration against oxidative gases (such as ozone, NOx and SOx) contained in the air in trace quantities (i.e., gas resistance).
With regard to the image fastness, what has hitherto been called to account is chiefly the discoloration of images that is due to sunlight or illumination of various types (i.e., light fastness), and the problem of such discoloration has been attempted to be solved by the use of dyes having good light fastness. However, in recent years, as images are made to have higher image quality, there have increased opportunities to exhibit images in rooms. Hence, the color change or discoloration caused by oxidative gases contained in the air (or the gas resistance) has become considered to be an important problem together with the light fastness.
In recent years, as a recording medium for ink jet recording, a recording medium is also used in which an ink receiving-layer containing a pigment and a binder is formed on a base paper in order to improve sharpness of ink color, color tone reproducibility and optical density. This, however, is desired to be improved because images formed on such a recording medium may show serious color change or discoloration, in regard to the gas resistance.
Japanese Patent No. 02919615 and Japanese Patent Publication No. H08-26263 disclose a proposal to improve color tones and remedy color change or discoloration against ozone gas. However, such gas resistance is required to be more improved in the ink jet recording method in recent years that can obtain recorded images having so high image quality as to be comparable to that of silver halide photographs.
Besides the improvement in image fastness, it is also required to improve image density (optical density) in order to achieve sufficient gradation and depth of shadow area in the case when images are formed on the recording medium in which a porous material such as alumina or silica is used as an ink receiving material.
Japanese Patent Application Laid-Open No. 2000-290552 discloses a proposal to use an ink containing specific two types of dyes, in order to improve image density. Japanese Patent Application Laid-Open No. 2000-318300 also discloses a proposal in which a treating agent containing a polymeric substance is applied to a recording medium and thereafter an ink containing a coloring material is made to adhere to the recording medium to thereby cause the coloring material to aggregate so that the image density can be improved. Japanese Patent Application Laid-Open No. 2002-275380 and No. 2003-292808 further disclose a proposal to improve image density by using a novel disazo or trisazo dye.